LX2201 Datasheet, PDF (8/11 Pages) Microsemi Corporation – USB Li-Ion Battery Charger

LX2201
TM
®
USB Li-Ion Battery Charger
PRODUCTION DATA SHEET
THEORY OF OPERATION
GENERAL DESCRIPTION
TOP OFF CHARGE MODE
The LX2201 is designed to charge a single cell Lithium
Ion battery using two steps: a constant current step
followed by a constant voltage step. The basic charger
function uses the VDD pins as an input and BAT pins as
the output. The LX2201 charger has a programmable
maximum current (programmable by the resistor value
between pin CCP to GND) which is the maximum
charging current during the Constant Current Mode of the
charging profile. The low dropout of the pass element
allows the battery to be charged from a loosely regulated
power supply. In the Constant Voltage Mode, the battery
terminal voltage can be regulated to 4.1V or 4.2V by
strapping the VM pin to VDD or GND, respectively. The
charger will terminate constant voltage charging once the
current drops below the minimum current setting
(programmable by the resistor value between pin CTP to
GND).
The LX2201 has an integrated thermostat with a linear
thermal regulation loop that will throttle back the charging
current to prevent the internal die temperature from
exceeding 150ºC. This feature prevents damage to the
system board when the IC exceeds its thermal temperature.
CURRENT CHARGE MODE
A conditioning current is applied to batteries that are
deeply discharged and have a terminal voltage less than
60% of the constant voltage level. The conditioning current
is 5% of the CCP programmable constant current level
(except where it might be limited in the USB states). Once
the battery terminal voltage exceeds the 60% level, the full
constant current level is applied (unless charging current is
limited by one of the other charger control loops).
CHARGE TERMINATION MODE
Once the charger has completed a charge cycle, if
power remains applied, the LX2201 enters a Voltage
Monitoring mode. In this mode the LX2201 monitors the
battery terminal voltage and applies a top off charge if the
battery voltage drops by more than 3% of full scale. This
feature is especially important for charging systems in
equipment where usage is infrequent.
USB CHARGE MODE
The LX2201 is fully compliant with, and supports, the
USB specifications – the Low Power Peripheral (100mA)
and High Power Peripherals (500mA). VID1 logic input
selects USB charge currents. The LX2201 senses the
current flowing from the VIN terminal to the VDD
terminal; then it limits the VIN current by reducing the
current flowing from V_DD to V_BAT. Note: the USB
Charge Limit circuit does not limit the input current and
only scales the charging current.
DISCHARGE MODE
In discharge mode, VID0 is, indicate discharge mode
enable. The system load is connected to VDD. The input
power is connected to VDD through an internal diode.
When the input power is removed, the battery current
flows from V_BAT to VDD. The circuit of Figure 3 shows
the LX2201 in a discharge mode configuration with both
AC adapter and USB inputs. The USB input is diode
ORed to the VDD pin and uses a MOSFET to reduce the
diode drop across the ORing diode. The LX2201 provides
a signal “PSW” to control the MOSFET for charge and
discharge modes. When both AC and USB power are
applied the PSW signal is overridden by the AC adapter
diode and the MOSFET is turned off
To increase system battery life and avoid float charging,
the LX2201 turns off the pass element once the battery has
been fully charged. The charge termination state occurs at
the end of constant voltage mode. The charge status
changes state when charging is completed.
Copyright © 2000
Rev. 1.2b, 2005-04-13
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
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